Method of producing high tenacity regenerated cellulose yarns



April25, 1950 w. J. ELVIN ETAL 2,505,033

METHOD 0F PRODUCING HIGH-TENACITY REGENERATED CELLULOSE YARNS Filed May 1. 1945- IN V EN TORS 'WILLIAMJ. ELVIN. B JOHN B. STEIDING.

Y wi j m ATTORNEYS.

Patented Apr. 25, 1950 METHOD OF PRODUCING HIGH TENACITY BEGENERATED CELLULOSE YARNS I William J. Elvin, Frostburg, and John B. Steiding,

Midland, Md., assignors to Celanese Crpora-. tion of America, a corporation of Delaware.

Application May 1, 1945, Serial No. 591,382; 7

4 Claims. (01. 81-130) This invention relates to the preparation of high tenacity regenerated cellulose yarns, and relates more particularly to improved saponification methods for the production of said high tenacity regenerated cellulose yarns from stretched yarns having a basis of cellulose acetate, or other or-. ganic ester of cellulose.

An object of this invention of regenerated cellulose yarns of higher tenacities by a process involving the saponification of stretched yarns having a basis of cellulose acetate or other organic ester of cellulose.

Another object of this invention is the pro-. vision of an improved saponification processior the production of said regenerated cellulose yarns from stretched yarns of cellulose acetate or other organic ester of cellulose wherein higher yarn tenacities with lim ted weight loss of the -saponi-' fied yarns are obtained.

A further object of this invention is the provision of improved apparatus for the continuous, saponification of yarns, and more especially, stretched yarns having a basis of cellulose acetate or other organic ester of cellulose, wherein means are provided for controlling the tension exerted thereon.

Other objects of this invention will appear'from the following detailed description and the accompanying drawing.

In the drawing, wherein a preferred embodiment of our novel apparatus for carrying out our invention is shown,

Fig. 1 is a plan view of an improved apparatus" for the continuous, controlled saponification of cellulose acetate or other organic ester of cellulose yarns, v

Fig. 2 is a side elevational view, partly in section, of this apparatus showing th roller system in askewed relation, and

Fig. 3 is a plan View, onan enlarged scale of one of the rollers employed in our novel continuous saponification apparatus. i e

Like reference numerals indicate like parts throughout the several views of the drawing.

Yarns of regenerated cellulose of high tenacity have been produced by the saponification of stretched yarns having a basis of an organic esterof cellulose, such as, for example,"cellulose ace tate. The stretching of the yarns is effected dur-' ing' some stage in'their manufacture and the yarns may be increased in length as a" result-of the stretching operation to the extent of 200, 300, 500, or even 1000 or 2000% of their original length. The yarns acquire a" relatively high tenacity on bein stretched, the tenacity being retainedzand inman y instances enhanced by saponification' is the preparation which, as is well known, effects a regeneration. .of the cellulose. Theresulting high tenacity re-' generated cellulose yarns are of great strength and find extensive employment where yarns of an unusual degree of strength and dimensional.

stability are desired.

During the saponiflcation of the stretched cel-. lulose acetate or other. organic ester of cellulose yarns, the latter undergov various physical and chemcal changes. One important physical change which the stretched cellulose acetate.

yarns undergoduring saponification is an increase in length at the start of saponification due to linear as well as lateral swelling of the yarns as they are wet out followed by marked linear shrinkage involving an appreciable decrease in length. The shrinkage varies depending upon the nature of the stretched. product undergoing saponification. A considerable loss in the weight of the cellulose acetate yarns also takes place due to the fact that the acetyl groups present are split oiT by the saponifyin agent employed. Moreover, this chemical change causes the yarns to undergo a pronounced decrease in denier which, because the breaking. load is usually retained, produces yarnslof substantially increased.

tenacity. An additionalweight loss also takes place by reason of the factthat certain alkali-,

soluble fractions of the regenerated cellulose produced are removed as .well, Such weight and shrinkage losses decrease the yield of regenerated cellulose yarn which may be obtained from a given quantity of stretched cellulose acetate yarns which decreaseis, of course. undesirable. 7 We have now discoveredthat regenerated cellulose yarnsof superior physical characteristics may be obtained with a minimum weight loss by an improved saponification process. In accordance with our novel saponification process, the stretched cellulose acetate or other organic ester of cellulose yarns are saponified under a predeterm ned and controlled tension so that the ultimate shrinkage effected during saponification is held Within predetermined limits, whereby the shrinkage effected as a result of the saponification reaction is less than that normally produced when such'yarns are saponified in a relaxed condition, e; g. in the absence of tension, and allowed to shrink freely. Surprisingly enough, this novel methodof saponifying cellulose acetate "or other organic ester of cellulose yarns, wherein the yarns are maintained under controlled tensionjduring saponification, vproduces substantially completely regenerated cellulose yarns of an even higher jtenacity then-are normally obtained with the same cellulose acetate yarns, but saponified in the saponifying bath and that the retention of 3 these cellulosic fractions in theregeneratedrceb lulose yarns obtained is responsible ;.for thejimproved pliability and softnesspossessed by the yarns obtained in accordance with our process. This explanation, however, is merelyatheoretical one and we do not wish to be bound'thereby.

The desired degree of control:over theshrink age of the cellulose acetate yarns is achieved by maintaining the yarns under predetermined tension during the progress of the saponification re action, which tension maybe obtained in any convenient manner. Thus, 'for example, the yarns may besaponifie'din a continuous manner while passing from one yarn guide to another in the saponifyingbathemployed, the yarnguides being spring loaded or otherwise adapted to maintain theyarnsunder'thedesired degree of tension at each stage of the sapon'ification.

"Preferably, however, the yarns undergoing saponificationtare maintained under thedesired. controlled tension. by being passed continuously from one driven roller to another, partially or wholly submerged'in thed'esired saponifying bath. Tothis end we employ'a novel apparatus comprising a plurality of rollers the contour of which is such asto permit: some shinkage of the yarns to take place during the saponification process, but at thesame time, to maintain the yarns under a continuous :and predeterminedamount of tension at each stage of the saponification operation, whereby the total degree of shrinkage taking place is limited, and is less than that effected when.

theyarnsare saponifled in a completely relaxed condition.

of yarn 5 across the sections of rollers i5 and I generally indicated by the letter A. The sections A are of gradually increasing diameter, and thereact to take up any increase in the length due to relaxation of the yarn. As the saponiiy action of bath l begins to effect yarn 5, the lat e gradually begins to shrink. The rollers 7e and however, are rotated at such speed in timed relation to the rate of saponification that w...en this phase of the saponification is reached the yarn 5 is passing oversection B of said rollers. This section is n-ottapered but is substantially cylindrical in form since while passin over section jB therateofshrinkage is not sufficient to r quire .a changein the, contour of the roller to eliminate the excessive development of tension due to shrinkage. iI-Iowever, since the yarn continues to shrinkasit undergoes further saponification, increasing degree of tension is placed upon the yarn due to the unyielding rollers. Accordingly, as saponification proceeds further, the yarn undergoing saponification gradually moves .in a lateral direction across the contoured rollers 6 and i, still in timed relationship'to the degree of saponificaticaand finally reaches section C of said rollers which section is provided with a suitable taper. The taper of section C is such that it enables the yarn. to shrink but at the same time maintains it under-the desired tension. The contour of section 0 is such as to compensate 'for a grad ually increasing rate of shrinkage and'thi revents the tension on the yarn from building up to an undesirably high level. The 'substait' completely sapcnified yarn leaving roller '5 may be washed, neutralized'and dried in a continuous manner, or the yarn may be'taken up in the form of a suitablepackage and the yarn maybe new tralized, washed and'dried in. package form. Bur

. ing drying, the yarn may be allowed'to mini;

the greater will be the degree of shrinkage ef- Referringnow' to the drawing, astretched ceilulose acetate .yarn 5 coming "from a suitable sourceof supply (notshown) is passed, as .many times asdesired, around a pair of identical rollers 6. and. l .mounted-on shafts .8 and ,9 respectively, the shaft .9 fcarryingroller lgbeing somewhat askewwith respect .to shaft 8.. .The rollers iend IV are ,shownaon. asomew-hat enlargedscale .inJiig. 3. Shafts-8 and Son whichthe rollers are mounted-are provided withrsuitable drivingmeans not shown) so that they maybe driven at any -desired speed, thus continuously advancing :yarn 5 through the-:bath. Themethod of mounting shafts 3 and 9 so; that. shaftx9.-.-is-notparallel vtc shaft lL-gives alead to-the-yarnpassing around said rollers and not only @keepsthe ,yarn wraps apart :but also causes yarn :5 to move laterally alongthe surface of the rollers. Rollers 6 and l are partially submerged in a saponifying bath l5 ofany suitable composition whichiis contained inatroughil Asstated, the rollers 5 and! may, ifidesiredyalso be wholly-submerged in bath ii thus'maintaining the'cellulose-acetate yarn 5 in constant contact with-the saponifying bath 0.

towet out yarn 5. "This' actionttends 'totrelax the stretched yarn-5.'somewhat,'permittingit to in the yarn to compensateffor'anyincrease inlength.

This' take-np is effected by the lateral-movement fected during drying.

The tensions under which theyarns aremaintained during thestages of the saponification operation whereby -the degree of shrinkage they undergo is limited, may be irom'0.02 to 05 gram per denier'but optimum results are achieved when aqueous-alcoholic. solutions. :Advantageously, the

hydroxide are employed as the saponifying agent, the sodium hydroxide may be presentin.

a, concentration of from 0.lto 5% by weight and saponification may-beefiected in-from 1 to 69 minutes: with" the solution; at a temperature of from '30;to C. whenemploying aqueous solutions :of sodium hydroxide; as the saponityingg medium, it is preferable to include a salt such as sodium sulfate or sodium acetate in said solution.

To eifect the desired saponiflcation the stretched yarns are led directly into the saponifying bath, the path through the saponiiying bath being sufficiently extended and the speed at which the yarns pass'through thebath being such that the yarn, under the conditions of both" temperature and concentration employed,- is

completely saponified before leaving the; bath-L Speeds of 10 to 100 meters per minute are satisfactory.

'While our invention hasbeen more particularly described in connection with con'tiriiious saponiflcation processes, batch processes "may tension.

In order further to illustrate our invention but without" being limited thereto the following example is given:-

Example A 144 denier, 12o filament celluloseacetate yarn, which has been prepared by subjecting a d 1440 denier yarn to a 10 times stretch, is saponifled in a continuous manner at 80 C..with a saponifying bath comprising a 0.7% aqueous solution of sodium hydroxide containing 8.5% by. weight of sodium. acetate. The yarns are passed through the saponifying bath at a speed of 10 meters per minute and the path of the yarn is of. such extent that itissubjected to the action of the saponifying bath for 11 minutes. During sa oniflcation the yarns passing through the bath are maintained under a continuous tension in the manner heretofore described,-employing a pair of driven, novel contoured rollers around which the running yarn ispassed. The initial taper of the rollers is such that as the yarn pa ses into the bath it is placed under tension with the taper of the rollers extending the yarn path to avoid the formation of any slack; because of the relaxing or swelling effect of the initial wetting. The slackening permits the yarn to increase about 0.35% in length which 15.01: course, taken up the increasing diameter of the contoured rollers. The tension under which the yarn is maintained amounts to about 0.03' ram per denier. The loops are then led across the tapered rollers in timed relation to the shrinkage and to the saponiflcation. The contour of the rollers is such that the yarns are also maintained under a substantially uniform tension of 0.03 gram per denier during the initial saponiflcation across the flat portion of the rollers as well as during the latter stage of saponiflcation across the final tapered portion. The degree oi. shrinkage permitted by maintaining the yarns under tension is thereby limited to about 0.35% of the original yarn length, a total change in length of 0.70% taking place when determined from the initial, relaxed state. The saponified, regenerated cellulose yarns obtained are washed, neutralized with a 1% aqueous solution of acetic acid, washed and dried at 80 C. to a moisture content of 0.75%. The regenerated cellulose yarn produced is of about 100 denier, has a dry tenacity of 7.3 grams per denier and a wet tenacity of 6.5 grams per denier. The over-all linear shrinkage of the yarn from its original length is found to be only 0.9%, a shrinkage of 0.55% having occurred during drying to the particular moisture content inlike saponiflcation, said yarn shrinks about 0.55% T in length due to the saponiflcation and a total of 1.45% when dried to a like moisture content, a shrinkage of 0.9% taking place as a result of drying. The weight loss of the yarns saponified under tension in accordance with our novel process amounts to about 37.5% while the weight loss for like cellulose acetate yarns saponified under the same conditions but in a relaxed state amounts to about 40%.

The cellulose acetate or other organic ester of cellulose yarns which may be stretched and then saponified in accordance with our novel process toyield regenerated cellulose yarns of improved tenacity may be prepared by extruding a solution of cellulose acetate or other organic ester of cellulose dissolved in a suitable volatile solvent, through a plurality of orifices into an evaporative medium as in the dry method of spinning, or into a coagulating or precipitating liouid medium as in the wet method of spinning. The filaments formed in this manner are associated together to form the desired multi-filament yarn or thread which is, first stretched and then saponified.- In addition to cellulose acetate, other organic esters of cellulose which may be employed for the preparation of the yarns are, for example, cellulose propionate, cellulose butyrate, and mixed esters such as, cellulose acetate-propionate and cellulose acetate-butyrate.

The cellulose acetate or other organic ester of cellulose employed may be of any degree of esterification. For example, in the case of cellulose. acetate materials, they may have an acetyl value of from 40 to 62%, calculated as acetic acid.

After the yarn or thread is formed, it is then stretched. This is usually done when the yarn is in a somewhat softened condition. The yarn may be so tened by trea ing it with a solvent,

; latent solvent. or swelling agent for the cellu ose or padding methods, or b exposing the celluloseacetate materia s to vapors of said organic solvents, latents solvents or swelling agents during, or just prior to. the stretching operation. The yarns ma a so be softened by radiant heat or by the use of steam or hot water. After softening, the yarns may be stretched in a continuous manner by being passed from a roll which rotates at a slow speed to one rotating at a higher speed, the ro ler rotating at a h gher s eed serving to give the yarn the desired stretch. The de ree of stretch ma be vari d by increasing or decreasing J the differential in the speeds of the rollers. The

yarn may be stretched in a p urality of sta es, if desired. For example, part of the stretch may be imparted to the yarn by softening and stretching in one sta e and the remainder of the stretch may be imparted by a second softening and stretching operation, but more than two s ages of stretch may, of course, be emplo ed. A ter s retching the yarns ma be taken up on bob ins or ma be collected in a centrifugal spinning box or Topham box and are ready for saponiflcation in accordance with our novel process.

It is to be understood that the foregoing detailed description is given merely by way of illustrat on and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

1. In a process for the production of improved dicated. When allowed to shrink freely during high tenacity regenerated cellulose yarns by the saponification of :str-etched yarns having -a basis of an organic ester 70fv cellulose, wherein-the yarns undergoing saponification increase in length :and then 'decrease :in length :as said rsaponification proceeds, the step which scomprlsescontinuously feeding said organicester-ofecellulose yarns into a' saponifyingbathand placing the -wetted yarns under a controlled and predetermined-tension.of 0.02 to 0.5 gram 'persden-ier' in the saponifying bath throughout the entire asaponificatmn ,process, whereby the degree of shrinkage eflected-by the saponification reaction-is limitedto vlessithan that-reflected when said yarns are.saponifiedina substantially untensionedrcondition.

2. In -aprocess for ,thelproduction.oflimproved high tenacityregenerated;cellulose.yarns by the saponification of stretchedyarns havinga basis of celluloseacetate, wherein they-ems undergoing saponification increase .in -length .and .then. decrease in-length as said saponiflcatlonproceeds,-

the step "which comprises continuously .feeding said celiulose acetate yarns .into vawsaponifying bath and placing :the @wetted yarns :under .a controlled and predetermined tens-ion.of 0.02 to 0.5 gram per denier in'the saponifying bath throughout-the entire saponificationiprocess, Wherebylthe degree of shrinkage .efiected Joy-the saponification-reaction is limited toless than that effected when said yarns are saponified in a substantially untensioned condition.

.3. In a process for the productionof improved high tenacityregenerated celluloseyarns by the saponification of" stretched ,yarnshaving a, basis of celluloseaacetate, wherein the yarns undergoing saponificationlincrease inlength and then decrease in --length as said saponification proceeds, the step which comprises continuously feeding said cellulose acetate yarns into alsaponifying.

bath comprising an aqueous alkaline medium and placing the wetted yarns-under a controlled and predetermined --tension of-0.02 to 0.5 gram per denier in the saponifying bath throughout .the entire-saponification process, whereby thedegree 0f'-.shrinkage effected by thesaponificationlreactionis li-mitedtoless than that effected whensaid yarns are saponified in a substantially untensioned condition.

.4. In a process-for the production of improved hightenacity. regenerated cellulose yarns "by-the saponification :of stretched yarnshaving a basis of cellulose acetate, wherein the yarns undergoing saponificationincrease in.-1ength--and=then decrease in length as-said saponification proceeds, the step which comprises continuously ifeeding said cellulose {acetate yarnsinto -a saponifying bath comprising an aqueous solution of sodium hydroxide and placing the wetted yarns under: a controlled and predetermined tension of 0.02 :to 0.5 gram per denier :in the saponifying bath throughout the *entire saponification process, whereby the degree. of shrinkage efiected by-the saponification reaction. is limited to less than that efiected when said yarns are seponified in asubstantiall-y untensioned condition.

WILLIAM- J. ELVIN. JOHN B.-SEI-EIDING.

REFERENCES CITED The following-references are-of record in the fileof .this patent:

UNITED STATES PATENTS 

1. IN A PROCESS FOR THE PRODUCTION OF IMPROVED HIGH TENACITY REGENERATED CELLULOSE YARNS BY THE SAPONIFICATION OF STRETCHED YARNS HAVING A BASIS OF AN ORGANIC ESTER OF CELLULOSE, WHEREIN THE YARNS UNDERGOING SAPONIFICATION INCREASE IN LENGTH AND THEN DECREASE IN LENGTH AS SAID SAPONIFICATION PROCEEDS, THE STEP WHICH COMPRISES CONTINUOUSLY FEEDING SAID ORGANIC ESTER OF CELLULOSE YARNS INTO A SAPONIFYING BATH AND PLACING THE WETTED YARNS UNDER A CONTROLLED AND PREDETERMINED TENSION OF 0.02 TO 0.5 GRAM PER DENIER IN THE SAPONIFYING BATH THROUGHOUT THE ENTIRE SAPONIFICATION PROCESS, WHEREBY THE DEGREE OF SHRINKAGE EFFECTED BY THE SAPONIFICATION REACTION IS LIMITED TO LESS THAN THAT EFFECTED WHEN SAID YARNS ARE SAPONIFIED IN A SUBSTANTIALLY UNTENSIONED CONDITION. 